U.S. patent number 3,967,904 [Application Number 05/541,741] was granted by the patent office on 1976-07-06 for precision radiation source regulation circuit.
This patent grant is currently assigned to Electronics Corporation of America. Invention is credited to Phillip J. Cade.
United States Patent |
3,967,904 |
Cade |
July 6, 1976 |
Precision radiation source regulation circuit
Abstract
A precision lamp regulation circuit includes a source of AC
power, a lamp connected in circuit with the AC source, a transistor
switch connected in circuit between the AC source and the lamp, a
light sensor optically coupled to respond to the radiation output
of the lamp, circuitry for placing the transistor switch in
conducting condition at the beginning of a half cycle of applied AC
power, and a feedback circuit responsive to the light sensor for
placing the transistor switch in non-conducting condition to
terminate energization of the lamp during that half cycle of
applied AC power.
Inventors: |
Cade; Phillip J. (Winchester,
MA) |
Assignee: |
Electronics Corporation of
America (Cambridge, MA)
|
Family
ID: |
24160840 |
Appl.
No.: |
05/541,741 |
Filed: |
January 15, 1975 |
Current U.S.
Class: |
356/432; 315/158;
323/236; 250/205; 315/159; 323/902; 323/903 |
Current CPC
Class: |
H01L
25/167 (20130101); Y10S 323/902 (20130101); Y10S
323/903 (20130101) |
Current International
Class: |
G05D
25/02 (20060101); G05D 25/00 (20060101); G01N
021/22 (); G01J 001/32 (); H05B 037/02 () |
Field of
Search: |
;356/207,208,201
;250/205 ;315/158,159 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Phototransistor Regulates . . Intensity," Carvajal, Electronics,
vol. 38, No. 20, Oct. 4, 1965, p. 101..
|
Primary Examiner: McGraw; Vincent P.
Claims
What is claimed is:
1. A monitoring system comprising a source of AC power,
a radiation source connected in circuit with said AC source,
a transistor switch connected in circuit between said AC source and
said radiation source,
a radiation sensor optically coupled to respond to the radiation
output of said radiation source,
circuitry for placing said transistor switch in conducting
condition at the beginning of a half cycle of applied AC power to
apply power to said radiation source to cause said radiation source
to produce an increased radiation output,
and a feedback circuit responsive to said radiation sensor for
placing said transistor switch in non-conducting condition in
response to said increased radiation output of said radiation
source to terminate energization of said radiation source during
that half cycle of applied AC power so that the radiation output of
said radiation source is regulated with precision.
2. The system as claimed in claim 1 wherein said radiation source
is an incandescent lamp.
3. The system as claimed in claim 1 wherein said radiation sensor
is a semiconductor photosensor.
4. The system as claimed in claim 1 wherein said feedback circuit
includes stabilized high gain amplifier circuitry.
5. The system as claimed in claim 1 and further including an
optical system for focusing radiation from said radiation source in
a narrow beam for transmission across a channel, a second radiation
sensor for disposition on the opposite side of said channel for
sensing radiation in said radiation beam, and output circuitry
responsive to said second radiation sensor for providing an
indication of the flow of matter in said channel across said
radiation beam.
6. The system as claimed in claim 1 wherein said radiation sensor
includes a semiconductor device connected in circuit with a
precision current source and said feedback circuit includes a
plurality of amplification stages and time delay circuitry for
delaying the switching of the output of said feedback circuit from
one output condition to another.
7. The system as claimed in claim 1 wherein said source of AC power
includes a step down transformer, said radiation source is a low
voltage incandescent lamp that is connected across the secondary of
said transformer, said radiation sensor is a reverse biased
semiconductor diode, and said feedback circuit includes stabilized
high gain amplifier circuitry connected to control current flow at
the base electrode of said transistor switch.
8. The system as claimed in claim 7 wherein said high gain
amplifier circuitry includes a plurality of amplification stages
and time delay circuitry for delaying the switching of the output
of said feedback circuit from one output condition to another.
9. The system as claimed in claim 8 and further including an
optical system for focusing radiation from said radiation source in
a narrow beam for transmission across a channel, a second radiation
sensor for disposition on the opposite side of said channel sensing
radiation in said radiation beam and output circuitry responsive to
said second radiation sensor for providing an indication of the
flow of particulate matter across said radiation beam in said
channel.
10. The system as claimed in claim 9 wherein said secondary of said
transformer has a tap to which said lamp is connected and further
including a second transistor switch connected to said secondary of
said transformer for controlling the energization of said lamp
during alternate half cycles of said source of AC power.
11. A system for regulating the output of a radiation source
comprising a power source terminal,
a radiation source connected in circuit with said power source
terminal,
a transistor switch connected in circuit between said power source
terminal and said radiation source to control the energization of
said radiation source,
a radiation sensor optically coupled to and responsive to the
radiation output of said radiation source,
and a feedback circuit responsive to said radiation sensor and
connected to control said transistor switch, said feedback circuit
in response to a first value of radiation output of said radiation
source as sensed by said sensor having a first output condition
that places said transistor switch in nonconducting condition to
terminate energization of said radiation source and then in
response to reduction of radiation output from said radiation
source to a second value below said first value as sensed by said
sensor having a second output condition that places said transistor
switch in conducting condition to again apply power to said
radiation source so that said radiation source is alternately
energized and de-energized as a function of its radiation output
and the radiation output of said radiation source is regulated with
precision.
12. The system as claimed in claim 11 wherein said radiation sensor
includes a semiconductor device and said feedback circuit includes
an amplification stage.
13. The system as claimed in claim 11 wherein said radiation source
is a low voltage incandescent lamp, said radiation sensor is a
reverse biased semiconductor diode, and said feedback circuit
includes stabilized high gain amplifier circuitry connected to
control current flow at the base electrode of said transistor
switch and time delay circuitry for delaying the switching of the
output of said feedback circuit from one output condition to
another.
Description
SUMMARY OF INVENTION
This invention relates to the field of testing and measurement of
physical phenomena and more specifically to circuit arrangements
for generating a stable radiation output for use in a monitoring
system.
The present invention provides a system for producing a stable
radiation output in an arrangement that has a long useful life, is
rugged and may be used over a wide range of ambient temperatures.
While it is anticipated that the invention may be useful in a
variety of testing, measuring and experimentation systems, a
particular application is in the monitoring of smoke output of
large burner systems in which an accurately defined beam of light
extends across the smokestack (smoke discharge passage) for
distances of up to thirty feet and greater to a detector positioned
on the opposite side of the smokestack. A particular concern is the
amount of visible particulate matter that is discharged into the
atmosphere and to that end it is desired to monitor the effect such
particulate matter has in the visible spectrum. The power
consumption of the monitoring system should be minimized without
impairing the stability of light output over a range of operating
conditions, including conditions of both temperature and energizing
voltage. The magnitude of the energizing voltage is of particular
concern as the light output is a function of the sixth power of the
applied voltage.
In accordance with the invention there is provided a precision
regulation circuit that includes a source of AC power, a radiation
source connected in circuit with the AC source, a transistor switch
connected in circuit between the AC source and the radiation
source, a radiation sensor optically coupled to respond to the
radiation output of the radiation source, circuitry for placing the
transistor switch in conducting condition at the beginning of a
half cycle of applied AC power, and a feedback circuit responsive
to the radiation sensor for placing the transistor switch in
non-conducting condition to terminate energization of the radiation
source during that half cycle of applied AC power.
This circuit provides a stable radiation output and has particular
application in a system for monitoring particulate matter in a
smokestack, output radiation from the lamp being focused in a
narrow beam that traverses the smokestack for detection on the
opposite side thereof. The circuit may be of half wave or full wave
type, a transistor switch commencing conduction at the beginning of
alternate half cycles of applied AC power in the half wave system
and at the beginning of every half cycle in the full wave system.
In particular embodiments of the invention the radiation source is
a low voltage (2.5 volts at 21/2 amperes) incandescent lamp that
has a rugged, compact filament and an output of about ten
candlepower. In such embodiments the filament is heated to
incandescence for generating light output in the visible spectrum
and a transistor switch is conductive at the beginning of either
every or alternate AC half cycles, and the light sensor responds to
the radiation output of the lamp to generate a feedback signal that
places the transistor switch in non-conducting condition after the
lamp has produced a predetermined light output during the initial
portion of its half cycle of conduction.
In operation, the transistor switch conducts with low voltage drop
at the beginning of a half cycle and applies AC electrical power to
the lamp. With the energization of the lamp filament, the radiation
output, after a slight thermal lag starts to increase rapidly. This
increasing radiation output is sensed by a semiconductor
photosensor which produces an output through an inverting high gain
stabilized amplifier to turn off the transistor switch. This
terminates the heating of the lamp filament and its radiation
output starts to decay. When the radiation level falls below a
preset threshold, the transistor switch is reconditioned and is
switched into fully saturated condition at the beginning of the
next half cycle for again supplying energy to the lamp and
repeating the cycle. A time delay included in the amplifier
circuitry prevents premature switching of the feedback signal.
Should the applied voltage from the AC source increase, the
photosensor will cause the transistor switch to turn off earlier in
the cycle and similarly should the applied AC voltage decrease, the
sensor will delay that turn off until later in the cycle. Thus the
system provides regulation of radiation output, a typical
regulation in a system for monitoring a smokestack being within 0.5
percent over a change in supply voltage of 30 percent, in a fast
acting arrangement of low power consumption.
Other objects, features and advantages of the invention will be
seen as the following description of particular embodiments thereof
progresses, in conjunction with the drawings, in which:
FIG. 1 is a block diagram of an embodiment of the invention;
FIG. 2 is a more detailed schematic diagram of the embodiment shown
in FIG. 1;
FIGS. 3A and 3B are simplified diagrams indicating aspects of
operation of the circuitry shown in FIGS. 1 and 2; and
FIG. 4 is a simplified schematic diagram of a second embodiment of
the invention.
DESCRIPTION OF PARTICULAR EMBODIMENTS
With reference to FIG. 1, lamp 10 is energized from an AC source in
the form of step down transformer 12 whose primary winding 14 has
terminals 16 connected to a suitable 60 Hertz source, the voltage
of which may vary over a range of 90-140 volts; and whose secondary
winding 18 provides an output of about 31/2 volts rms with 115
volts applied to primary 14. Connected in series between winding 18
and light source 10 in a transistor switch 20. Connected in across
winding 18 is a capacitor 22 and diode 24. The base 26 of
transistor 20 is connected to transistor 28 through resistor 30. A
bias resistor 32 is connected between base 26 of transistor 20 of
the junction between capacitor 22 and diode 24.
Optically coupled to radiation source 10 is a photosensor 40 in the
form of a reverse biased semiconductor diode. Inverting amplifier
circuitry 42 is connected to respond to the output of photosensor
40 and provides an output which is applied to the base 44 of
transistor 28. Terminals 46, 48 provide power connections between
the AC power source and the radiation source 10 and terminal 50
provides a feedback path connection. Lens 52 focuses the radiation
from source 10 in a narrow beam 54 which extends across the channel
56 being monitored (e.g. a smokestack) and a sensor 58 (e.g. a
semiconductor photosensor) is disposed on the opposite side of the
channel from lens 52 for sensing the radiation beam 54 and
generating an output that is applied to monitoring circuitry
60.
In this embodiment the light source 10 is an incandescent lamp that
has a tungsten filament 62 designed for energization at a nominal
voltage of 21/2 volts and a current of 21/2 amperes. A significant
portion of the radiation emitted by light source 10 is in the
visible spectrum and a filter 64 may be utilized for limiting
radiation in beam. Shielding 66 restricts the field of view of
sensor 40 to source 10.
A more detailed understanding of aspects of the embodiment shown in
FIG. 1 may be had with reference to FIG. 2. As indicated in that
figure, photosensor 40 is a reverse biased silicon diode that is
connected in series with a network of trimming resistors 70 and an
adjustable resistor 72 between bus 74 that is connected via
terminal 76 to a 15 volt regulated power supply source. A filter
capacitor 80 is connected across diode 40 and that diode is
connected via resistor 82 to the base 84 of transistor 86. The
collector of transistor 86 is connected via a voltage dividing
network of resistors 88 and 90 to the base 92 of transistor 94. The
collector 96 of transistor 94 is connected to the base 98 of
transistor 100 and the collector 102 of that transistor is
connected via resistor 104 to terminal 50. Capacitor 106 is
connected between the collector of transistor 100 and the emitter
of transistor 96. Feedback is provided by resistor 108 in parallel
with capacitor 110 to the base 84 of transistor 86. This circuit
filters pickup from rf sources, sparks and the like and also
imposes a time delay on the switching of the feedback signal
applied at terminal 50.
Connected to terminal 50 via input network which includes resistor
120 and capacitor 122 is the base 124 of transistor 126. Collector
128 is connected to the base 130 of transistor 132, and collector
134 is connected via resistor 136 to the base 138 of transistor
140. Collector 142 is connected via resistor 144 to the base 146 of
transistor 148; and emitter 150 is connected to base 44 of
transistor 28. The transistors 132 and 148 are connected to an
unregulated power supply at terminal 160. These transistor stages
amplify the feedback signal.
During operation, at the beginning of each positive half cycle as
indicated in FIG. 3A at point 170, transistor 20 is conductive and
thus connects the AC source to energize lamp 10. After thermal lag
of brief duration, reheating of filament 62 starts at point 172 as
indicated in FIG. 3B. The resulting exponentially increasing light
output is sensed by diode 40 and the reverse current produced by
the absorption of light at the PN junction of diode 40 increases,
reducing the current flow from the precision current source of
resistors 70, 72 so that transistor 86 turns off at a threshold
value that is a function of the setting of adjustable resistor 72.
With the turn off of transistor 86, transistor 94 is turned off and
transistor 100 is turned on applying a feedback signal transition
through terminal 50 to the base of transistor 126 switching that
transistor on. That action switches transistor 132 on which in turn
turns transistors 140, 148 and 28 off to turn off transistor 20 at
point 174 (FIG. 3A) abruptly terminating the flow of current to
lamp 10. The filament 66 cools reducing the light output along the
exponential path indicated at line 176 of FIG. 3B. The reverse
current through diode 40 decreases so that after a time delay,
transistor 86 is turned on resetting the network and placing
transistor 28 in condition for conduction at the commencement of
the next positive half cycle at point 178. At that point transistor
20 is turned on, again supplying power to the filament of lamp 10
and increasing output radiation. This circuit provides accurate
regulation of the light output independent of changes in conditions
such as the amplitude of the applied voltage, the ripple in the
light output being in the order of 3-5 percent.
In the circuitry of FIG. 2, line voltage changes of 30 percent
cause a change in light output of less than 0.5 percent. The lamp
filament 62 is maintained essentially at a constant temperature
with resulting stability in spectral characteristics and the
relationship of intensity of all different colors radiated by the
lamp 10. This would not be the case if the lamp output were
regulated by changing the optical aperture or if the receiver
sensitivity were compensated by comparing the light output in the
smoke path with the light output when directly viewing the lamp.
Also, this regulating system in holding the light output constant,
provides compensation for film deposits on the lamp bulb which
normally occur throughout the life of the lamp as filament material
is evaporated and deposits form on the inner surface of the bulb.
The regulator is fast-acting, responding in less than one cycle of
the supply current, and operates with a high efficiency which not
only lowers the power consumption of the device but makes it easier
to dissipate the heat generated by losses within the device. For
instance, the transistor 20 has a voltage drop of less than 0.3
volts whereas a silicon controlled rectifier of comparable size
would have a voltage drop of as much as 2 volts.
A full wave arrangement illustrated in FIG. 4 includes a
transformer secondary 18' that has a center tap 190 and two
transistor switches 20', one connected to each terminal of
transformer winding 18'. Lamp 10' is connected across the
transformer secondary and sensor 40' provides a signal through
inverter amplifier circuitry 42' to transistor switch 28' whose
collector is connected through resistor 30' to the bases 26' of the
two transistor switches. At the beginning of each half cycle a
transistor switch 20' is conductive and is turned off during that
portion of each half cycle in response to turn off of switch 28'
that is responsive to sensor 40'.
While particular embodiments of the invention have been shown and
described, various modifications of the embodiments will be
apparent to those skilled in the art, and therefore it is not
intended that the invention be limited to the disclosed embodiments
or details thereof and departures may be made therefrom within the
spirit and scope of the invention.
* * * * *